Process for producing mica powder



Oct. 27, 1931. J. DAVENPORT PROCESS FOR PRODUCING MICA POWDER Filed Nov.30

Patented Oct. 27, 1931 v PATENT OFFICE JOHN DAVENPORT, OF FRANKLIN,NORTH CAROLINA.

PROCESS FOR PRODUCING MICA POWDER I Application filed November 30, 1928.Serial No. 322,734.'

This invention relates to improvements in processes for grinding mica,and the principal object thereof is to provide a process for producingmica powder or ground mica without'substantially impairing thelight-reflecting surfaces of the particles thereof, and with as completea delamination of the individual mica powder particles'as possible.

Mica powder is largely used in ornamentation to provide a sparklingsurface. Among many of such uses it may bemen- 1 tioned that dry micapowderis blown or siftpowder for moulds, particularly rubbermoulds towhich it is adapted because it will not unite with the rubber or rubbercomposition. It may also be employed to prevent adhesion between theinner tube and casing of automobile tires and may further'be used forlubrication and other purposes which are well known to those skilled inthe commercial arts.

By the present invention it is possible to produce mica powder of suchgreater degree of fineness and delamination that it may be ness.Furthermore, the sparkle or sheen of successfully employed in manyinstances,

where commercial mica powder has heretofore been unadapted because ofits coarse-- the mica powder produced by the present process andapparatus is far superior to any which has heretofore been made becauseof the unimpairment of the light-reflecting surfaces of the mica powder.

'Pulverization of mica to produce a mica powder without substantiallyimpairing the light-reflecting surfaces thereof has hereto-.

fore presented great difficulty for if mineral mica is reduced to apowder. by crushing, abrasion. hammering, or other usual methods, thelight-reflecting surfaces of the mica particles become scratched,thereby losing their lustre and light-reflecting power. r

The present invention comprises a process for producing mica powder bytriturating fragmentary sheets of mica in a liquid by a rubbing actionoperable to delaminate the mica sheets by relative slippage of adjacentlaminations thereof and at the same time reducing the powdered mica to asubstantially impalpable powder, without impairing the light-reflectingsurfaces of the particles thereof. a

A further object of the invention is to provide a novel process fortreating the triturate to remove impurities and to insure the productionof a mica powder of uniform fineness.

A further object of the invention is to provide a novel method fortreating the liquidsupported triturate to produce a dry mica powder, anda further object of the inventlon is to provide a novel method forgrading the dry mica powder more rapidly than has heretofore been mumwaste y preventing dispersion of the mica powder from the exposedsurface. of the mass being graded.

These and other objects and features of the invention will more fullyappear from the ossible, and also with a minifollowing description andthe accompanying drawings and will be particularly pointed out in theclaims.

An illustrative embodiment of the invention is shown in the accompanyingdrawmgs, in which,

Fig. 1 is a view, mainly in diagrammatic form, of the various pieces ofapparatus em- 'ployed in the process;

of a portion of the bolting machine and showing the novel process bywhich the-fine material is separated from a thick layer of mica powderpassing over the bolting clot-h of sufiicient thickness to facilitatethe passage of the finer particles through the bolting cloth whilepreventing dispersion of the powder from the upper or exposed surface ofsaid layer.

The complete method may be generally described as comprising trituratingfragmentary sheets of mica mixed with a liquid by a rubbing actionoperable to delaminate the mica sheets by relative slippage of adjacent-This process and various steps in the process,

which in themselves are novel, are pointed out in the'claims.

Suitable apparatus for producing the process are illustrated in theaccompanying drawings. Many of the illustrated pieces of apparatusemployed in the'performance of the process are in themselves old asemployed in other arts, but are so arranged and operated as to producenovel functions peculiarly adapted to the present process, as willhereinafter more fully appear.

The grinding or pulverizing apparatus illustrated herein comprises arevolving tube or drum 1 havingat one end a hollow inlet shaft .2 and atits oppositeend a hollow outlet shaft 3 with suitable means, such as acentral gear 4., for rotating the drum from usual mechanism not shown.Fragmentary sheets of mica are placed in the hopper 5 and carried by anelevator 6 to a hopper 7- which delivers the fragmentary mica'upon anendless belt 8-which in turn delivers the same to .a chute 9 leading toa hopper 10 which com- .municates with the hollow the drum.

Liquid, such as water from a suitable source, is delivered to the chute9-b v a pipe 11 having a valve 12 by means of which the quantity ofwater thus delivered may be regulated. Desirably the mixture which isdelivered to the drum comprises approximately forty-five per cent byweight of mica and fifty-five per cent by weight of water,

but, of course, the relative proportions there of may be varied asconditions may require. The drum 4' is of the usual tube mill typehaving a tube of plate-iron which is partially filled with a massof'substantially non-abra: sive, preferably spheroidal, weights 13, seeFig. 2.

Any suitable weights or balls may be used. Preferably flint pebbles areemployed 1 Shaft 2 ing surfaces of the particles of mice. powder.

and the drumprovided with a liningof silex 14 or other hard non-abrasivematerial. It will, however, be understood that other suitable weightsand lining may be employed,

such as rubber balls and a rubber lining, or wooden balls or otherwooden devlces and a wooden lining, or any other substantiallynon-abrasive material which will accomplls'h the purposes hereindescribed and avoid.

staining the ground material.

The important feature of the present ihvention is to produce atrituration of the material by a rubbing action between the fragments ofthe material itself and between the weights and the material which willcause relative slippage of adjacent laminations of the mica sheets,-sothat the same will be separated without substantially abrading thesurfaces of the sheets or the particles to which reaches a position inwhich'the weights or balls will flow downwardly and during theprogressive rotation of the drum will provide'a continuous circulationduring which the movement of the weights or ball relatively to eachother and to the fragmentary mica sheets, together with the movement ofthe mica sheets relatively to each other and to the balls, will producethe desired delaminations of the sheets by slippage of adjacentlaminations upon each other and the pulverization of the laminationswithout scratching or otherwise impairing the minute light-reflecthepresence of-jw ater, or other suitable liquid, particularly if suppliedin proper proportion to the amount or weight of mica, is largelyinstrumental in effecting such de-* lamination.

It may be stated that if the drum is rotated at too great a speed, theweights or balls will be carried up along the surface of the ascendingportion of the wall of ,the drum and caused to cascade in a. pathgenerally indicated by the dotted line (a) in Fig. 2, and

such cascading will produce such an'undesirable impact of the weightsupon the mica sheets as to abrade, shatter, or otherwise re-.

duce the light-reflectingproperties of the faces of the minutepa'rticles, while if the drum is rotated still more rapidly the weightswill be carried farther upthe side as to produce a maximum slidingaction which occurs just under the speed of rotation at which thecascading action begins; forexample, in a tube mill having a diameter offive feet,the desired action takes place at a speed of approximately tenrevolutions per minute which is approximately one-third the speed atwhich such a tube mill is usually rotated for pulverizing mica andsimilar minerals such as cement in which the material is subjected tothe impact of cascading to a semi-liquid mass which flows through thehollow shaft at the outlet end of the tube. This semi-liquid massdesirably is delivered to a pump 16 by which it is elevated through apipe 17 and discharged into a hydraulic classifier or separator 18. Thehydraulic separator may be of a usual type comprising a conicalreceptacle having at its lower end a cylindrical extension 19 throughwhich water under pressure is supplied from a pipe 20 having therein aregulatin valve 21. The water is introduced into the "pipe 20 at suchrate as will cause a continuous overflow from the upper end of thereceptacle 18-into a suitable conduit or chute 22 and the finer micapowder will be carried over withv this overflow.

The fineness of the powder thus separated or classified may bedetermined by regulation of the amount of water supplied through, thepipe 20. The heavier portions of thetriturate, which fall to the bottomof the classifier 18, may be withdrawn through a suitable discharge tubeinto a conveyer 23 which preferably leads to a concentrating apparatus24 which serves .to separate foreign materials from the particles ofmica and the former then desirably are delivered through a chute 25 tothe hopper 7 from which they are returned to the tube mill.

The classified mica powder. which is discharged from the classifier 18through the chute 22, desirably is delivered to a thickener orconcentrator which' may be in the form of two similar sect ons, theupper of which is a cylindrical tank 26 which desirably is provided witha central rotating shaft 27 having at its lower end laterally andupwardly suitable chemicals, may be introduced into the thickener orconcentrator for the purpose of speeding up the settling of the micapowder and thereby to obtain a thicker partial concentrateand also toproduce a clearer water 'overflow.

The partially concentrated material and water in which it is suspendedpasses through a delivery pipe 31 to suitable mechanism for expellingthe water to provide a dry powder. I A novel means for rapidly dryingthe mica powder is illustrated in the accompanying drawings in which thepipe 31 communicates .with'a spray pipe 32 which extends longitudinallyof and is located in proximity to a drying drum 33. The drying drumdesirably has a hollow shaft 34 through which steam is introduced at asuflicient pressure, and consequently temperature, to heat the surfaceof the drum to the required temperature.

The mica powder laden water is projected The or sprayed upon the surfaceof the drum in I he form of a thin film which adheres to the drum andthe drum-is rotated at such slow 35, such as a screw conveyer 37 asillustrated in Figs. 1 and 3. The dry mica powder thus delivered fromthe drum is of usual commercial fineness and may be packaged forshipment. The present invention, however, comprises a novel grading ofthe mica powder to provide maximum uniformity.

In the embodiment of the invention illustrated in the accompanyingdrawings the mica powder is delivered by the screw conveyer 37 to achute 38 which leads to a hopper 39 from which the mica powder iscarried upwardly by an elevator 40 and delivered to a hopper 41 of abolting machine. The mica powder is delivered from the hopper of thebolting machine to a distributing roller 42 which spreads it in a thicklayer of substantially uniform depth upon an inclined reciprocatingbolt.

The bolt as illustrated herein comprises provided with a sheet metalplate. 43 from cloth 44 and from the bolting cloth 44 to a flat metalplate 45 by which it is directed I cloth and the plates leading theretoin a layer to a second bolting cloth 46. The material passing over theend of the bolting cloth 46 is delivered to a hopper 47 from which it isreturned by a suitable conveyer, such as a screw conveyer 48 tothehopper 39 from which it is carried by the elevator 40 to the hopper 41of the bolting machine. Thus the material, which is discharged from theend of the bolt is re-bolted until all of the fine mica powder containedin it has passed through the bolting cloth; The fine powder which passesthrough the bolting cloths 44 and 46 is collected in hoppers 49 and 50'respectively. The bolting cloth may be of any desired fineness, such forexample as from onehhundred to two hundred mesh per'square 1nc Thebolting screens desirably are enclosed in a casing 51 and all otherparts of the mechanismfor treating the dry powder also desirably areenclosed in a suitable-casing not shown.

If desired a dust collector, such as are used in flour mills andelsewhere, may communigatewith such casing through asuitable pipe Theoperation of the bolt embodying the present invention differs radicallyfrom usual bolting machines in which the material to be bolted is passedover the bolting cloth in a thin layer for the purposeof removingpractically all of the fine material which will pass through the boltingcloth during the time such layer is passing over it. In the presentinvention a thick layer of mica power is passed over the bolting cloth.The weight of this 'layer serves to hold the mica of the under facethereof firmly upon the bolting cloth and aids greatly in forcingthefine mica through the bolting cloth. The greater bulk of the: materialof the layer passes over the end of the bolt and is returned to thehopper of the bolting machine in the manner above described and againpasses over the bolt. By reason of this construction and operation it isfound that the speed of bolting or screening is very greatly increasedwithout modifying the uniformity of the bolted product.-

The mica powder is passed over the bolting of sufiicient thicknesstoenable its weight to cause the under surface of the layer to liecontinuously in engagement with the bolting cloth and plates and toprevent the tossingof the material and consequent dispersion of the micapowder from. the upper surface of the layer as distinguished from usualscreening operations in which the fine material is passed in a thinsheet over the screening ma te'rial and is so tossed by the vibration ofthe screen as to cause a considerable scattering or dispersion of thefine material.

It is found in practice that the mica powder produced by the process andapparatus above described is superior to mica powder heretofore producedin respect to the preservation of the light-reflecting surfaces of theparticles of mica, and the greater fineness and uniformity of theproduct. By virtue of the more eflicient delamination, the mica powderproduced by the process and apparatus herein described is of very muchlighter weight per cubic foot and consequently is of much greater valuewhen used for decorative, ornamental, and other purposes as abovedescribed.

It will be understood that variations in the process and in constructionof the illustrative apparatus for performing the process disclosedherein may be made within the spirit and scope of the following claims.

Having thus described the invention, what is claimed as new, and desiredto be secured by Letters Patent,- is:.

1. The process of producing mica powder,

tially non-abrasive, moving weights operable to delaminate said sheetsby relative slippage of adjacent laminations thereof.

3. The process of producing micapowder, without substantially impairingthe light-re- .fle'cting surfaces ofthe particles thereof,

which comprises mixing fragmentary sheets of mica and a liquid withsubstantially nonabrasive spheroidal weights and causing a continuouscirculation of the mass to produce a rubbing trituration withoutsubstantial impact operable to delaminate said sheets by relativeslippage of adjacent laminations thereof.

4. The process of c ontinuously producing mica powder, withoutsubstantially impairing the light-reflecting surfaces of the particlesthereof, which comprises mixing fragmentary sheets of mica with a aflowing stream of liquid and subjecting the mixture to rubbingtrituration without substantial impact of a mass of hard, substantiallynonabrasive, spheroidal weights. flowing transversely of the generaldirection of flow of the stream of liquid.

5. The process of. continuously producing mica powder, withoutsubstantiall impairing the light-reflecting surfaces of the par ticlesthereof, which comprises mixing fragmentary sheets of mica with aflowing stream of liquld and subjecting the mixture to rubbingtrituration of a mass of hard, substantially non-abrasive, spheroidalweights flowing transversely of t e general direction of flow of thestream of liquid and hydraulically separating'the mica powder from theheavier particles of the triturate.

6. The process of continuously producing mica powder, withoutsubstantiall impairin the light-reflecting surfaces 0 the partic esthereof, which comprises mixing fragmentary sheets of mi'ca with aflowing stream of liquid and subjecting the mixture to rubbingtrituration without substantial impact or abrasion, hydraulicallyseparatin the mica powder from the heavier partic es of the triturate,partially concentrating said mica powder, producing a spray of thepartial con'centrate, and evaporating the'water from the solid materialof said spray.

7. The roces f continuously producing mica pow er, withoutsubstantiallfy in the light-reflecting surfaces 0 the. partic esthereof, which comprises mixing fragmentary sheets of mi'ca with aflowing stream of liquid and subjecting the mixture to rubbingtrituration without substantial impact or abrasion, hydraulicallyseparatin the mica powder from the heavier artic es of the triturate,concentrating the mica owder, drying said powder and bolting t e samefrom a layer of suflicie'nt de th substantially to prevent dispersion ofsai powder over the ex osed surface oi said layer.

testimony whereof, I have signed my name to this spe'cification.

JOHN DAVENPORT.

impalr-

